The present invention relates generally to a print control apparatus, and more particularly to improvements in such a print control apparatus which is used in a printer for receiving command data generated by a computer and which develops the computer-generated command data into raster image data.
Conventionally, in a printer of the type concerned, a data space or capacity which is the equivalent of a one-page amount of two-dimensional raster image data to be printed is allocated on a semiconductor storage device (internal memory) of a print control apparatus provided in the printer. In the print control apparatus, command data such as character codes supplied from a computer are developed into raster image data, and are stored on the allocated storage area. The term "raster image data" is used herein to refer to image data (bit data) to be supplied to the printer for instructing the printer to plot individual picture elements or pixels to form each line (raster) extending along a print width. When the raster image data developing process has been completed to produce the raster image data for all the rasters of one page of print output and store the raster image data in the semiconductor storage device, a print mechanism of the printer is started and the developed raster image data are outputted to the print mechanism. Thus, the print mechanism prints one page as a unit.
However, a great improvement made in resent years on the resolution and picture quality of the printers has brought about a remarkable increase in the amount of the raster image data contained in one page. With this increased data size, the cost of the necessary semiconductor storage device and the entire equipment cost have increased considerably. Furthermore, due to various limitations involved in power consumption and electric drivability of semiconductors, and a maximum data size processable in a central processing unit (CPU), it has become practically impossible to manufacture a satisfactorily operable printer. In addition, when a large-sized printout is desired, a larger capacity semiconductor storage device must be provided.
Further, much longer time is spent in developing the raster image data onto such a large semiconductor storage device (memory). For instance, when a print output of size A4 is to be printed, if each pixel requires 1 bit data as in a conventional black-and-white laser printer and if the resolution of the desired print output is up to 12 pixel/mm, a 1 megabyte of semiconductor storage device is required. However, an A0-size printout with resolution of 12 pixel/mm and 24 bits/pixel (16,700,000 color/pixel) requires at least 500 megabytes of memory. This will result in an extremely increased equipment cost and much longer developing time which will make it difficult to produce a practically usable printing apparatus.